X-ray to visible image converter with a cathode emission layer having non-uniform density profile structure

Abstract

High quantum efficiency (≧5%) ultrafast (≦100 picosecond) and broad band (30 KeV to 80 KeV for medical application) X-ray photo-electron cathode, high gain X-ray real time image intensifier and portable low intensity real time projection type X-ray imagescope use new vacuum photo-electron devices. A new type X-ray photo-electron cathode has a specially designed alkali halide electron emission layer that makes possible high quantum efficiency, high speed and broad band X-ray photon detection. An X-ray photo-electron cathode followed by a direct coupled micro channel plate and an output phosphor display screen form a new type panel shaped direct view X-ray intensifier tube which can have both high spatial resolution (≧10 lp/mm) and high gain (≧10 4 ). The thickness of this panel shaped disc X-ray intensifier can be less than 1 cm. A portable real time projection X-ray imagescope which employs this new type X-ray intensifier and other devices (small x-ray tube, small built-in high voltage power supply) can be widely used for medical, industrial and security applications.

What is claimed is: 
     
       1. A direct conversion X-ray photo-electron cathode comprising: a thin substrate of aluminum;   a layer of secondary electron emissive alkali halide selected from the group consisting of CsI and CsBr and deposited on the thin substrate, said layer of secondary electron emissive alkali halide exhibiting a nonuniform density profile structure which decreases in density from a high density at an interface with the thin substrate to a low density at a surface of the electron emissive layer, whereby an X-ray image impinging on the thin substrate is converted to an equivalent electron image and enhanced by the layer of secondary electron emissive alkali halide.   
     
     
       2. A direct conversion X-ray image intensifier comprising: a direct conversion X-ray photo-electron cathode having a metallic substrate with a layer of secondary electron emissive material deposited thereon, whereby an X-ray image impinging on the substrate is converted to an electron image and enhanced by the layer of secondary electron emissive material;   a microchannel plate; and   an output phosphor display screen, such that an incoming X-ray image is converted to an equivalent electron image by the photo-electron cathode, enhanced by electron multiplication in the microchannel plate and caused to strike the phosphor on the output screen to produce a visible display of the image.   
     
     
       3. The X-ray image intensifier of claim 2, wherein the photo-electron cathode comprises: a thin substrate of aluminum;   a layer of secondary electron emissive alkali halide selected from the group consisting of CsI and CsBr and deposited on the thin substrate, said layer of secondary electron emissive alkali halide exhibiting a non-uniform density profile structure which decreases in density from a high density at an interface with the thin substrate to a low density at a surface of the electron emissive layer, such that an X-ray image impinging on the thin substrate is converted to an equivalent electron image and enhanced by the layer of secondary electron emissive alkali halide.   
     
     
       4. The X-ray image intensifier of claim 3, wherein the photo-electron cathode is spaced from the microchannel plate a distance or approximately 0.4 mm. 
     
     
       5. The X-ray image intensifier of claim 3, wherein the photo-electron cathode is deposited directly on the input face of the microchannel plate. 
     
     
       6. The X-ray image intensifier of claim 3, wherein the X-ray photo-electron cathode has a high density sub-layer of approximately 1-2 μm with the density falling between 50 to 100%, which is approximately 2-4 g/cm 3 , and a low density sub-layer having a density profile continuously decreasing from about 50-30% at an interface with the high density sublayer to approximately 2-5% density at an output surface. 
     
     
       7. The portable low intensity X-ray imagescope of claim 3, wherein the X-ray photo-electron cathode has a high density sub-layer of approximately 1-2 μm with the density falling between 50 to 100%, which is approximately 2-4 g/cm 3 , and a low density sub-layer having a density profile continuously decreasing from about 50-30% at an interface with the high density sub-layer to approximately 2-5% density at an output surface. 
     
     
       8. A portable low intensity X-ray imagescope comprising: a low intensity source of X-rays;   an X-ray intensifier including a direct conversion X-ray photo-electron cathode and a microchannel plate having a metallic substrate with a layer of secondary electron emissive material deposited thereon, whereby an X-ray image impinging on the substrate is converted to an electron image and enhanced by the layer of secondary electron emissive material;   a phosphor display screen adjacent said microchannel plate such that an incoming X-ray image is converted to an equivalent electron image by the photo-electron cathode, enhanced by electron multiplication in the microchannel plate and caused to strike the phosphor on the display screen to produce a visible display of the X-ray image; and   a power supply including a high voltage supply for the X-ray intensifier and the source of low intensity X-rays, for effecting the operation of the imagescope.   
     
     
       9. The portable low intensity X-ray imagescope of claim 8, wherein the photo-electron cathode comprises: a thin substrate of aluminum;   a layer of secondary electron emissive alkali halide selected from the group consisting of CsI and CsBr and deposited on the thin substrate, said layer of secondary electron emissive alkali halide exhibiting a non-uniform density profile structure which decreases in density from a high density at an interface with the thin substrate to a low density at a surface of the electron emissive layer, such that an X-ray image impinging on the thin substrate is converted to an equivalent electron image and enhanced by the layer of secondary electron emissive alkali halide.   
     
     
       10. The portable low intensity X-ray imagescope of claim 9, wherein the photo-electron cathode is spaced from the microchannel plate a distance or approximately 0.4 mm. 
     
     
       11. The portable low intensity X-ray imagescope of claim 9, wherein the photo-electron cathode is deposited directly on the input face of the microchannel plate. 
     
     
       12. The portable low intensity X-ray imagescope of claim 9, further comprising a common base supporting said low intensity source of X-rays and said X-ray intensifier, said X-ray intensifier being positioned from said low intensity source of X-rays on said common base a distance which provides for the total interception of a cone of X-rays from said low intensity source by said X-ray intensifier, said power supply being contained within said common base.